Glutathione S-transferase (ligandin) from human and rat tissue will be isolated by GSH-affinity chromatography. The multiple catalytic activities and bilirubin binding properties will be investigated. Particular attention will be devoted to analyzing the conformational changes exhibited by the transferases and the nature of the regulation of the conformational events by protein-protein interactions of a collisional nature. The transferases may be useful models for receptors. The bilirubin binding properties of Z-protein, albumin and Alpha-fetoprotein will be compared with those of the transferases. The role of the transferases and Z-protein in the metabolism of bilirubin will be examined.